Researchers at Stanford University have found a new way of charging lithium-ion cells at different rates increases EV battery pack life. There is less overall deterioration from fast charging.
The research, published in IEEE Transactions on Control Systems Technology (shows abstract, article is behind a paywall) and reported on here, discovered that actively managing the charge to each cell can minimise overall wear and tear.
The approach means each cell can have a longer life. A battery pack may contain hundreds, even thousands, of cells.
According to the researchers:
- they formulated and solved a multiobjective fast charging-minimum degradation optimal control problem (OCP) for a lithium-ion battery module. It was made of series-connected cells equipped with an active balancing circuitry
- The proposed OCP is formulated:
- same charging time (OCP-SCT) and
- different charging time (OCP-DCT). The former assumes simultaneous charging of all cells irrespective of initial condition. The latter allows for different charging times based on cell condition.
“Results show that the OCP-DCT scheme provides more flexibility to deal with heterogeneity, boasting of lower temperature increase, charging current amplitudes, and degradation,” they said in their article.
A comparison with the common practice of constant current charging over a long-term cycling operation shows promising savings, they said. This is in terms of retained capacity, attainable under both control (OCP-SCT and OCP-DCT) schemes.
Stanford professor and senior study author Simona Onori said:
- initial simulations suggest batteries managed with the new technology could handle at least 20% more charge-discharge cycles
- this is even with frequent fast charging.
“If not properly tackled, cell-to-cell heterogeneities can compromise the longevity, health and safety of a battery pack and induce an early battery pack malfunction,” Onori reportedly said. “Our approach equalises the energy in each cell in the pack, bringing all cells to the final targeted state of charge in a balanced manner and improving the longevity of the pack.”
Photo: Simona Onori: “Our approach equalises the energy in each cell in the pack, bringing all cells to the final targeted state of charge in a balanced manner and improving the longevity of the pack.”